The invention relates to an inker unit for a high-speed rotary printing press comprising an endless ink transfer band arranged between an ink fountain roller and an ink transfer roller.
In a printing press, ink feeding systems are designed to transfer ink from an ink fountain to an ink distribution system in accordance with the requirements of a printing form.
The principle of intermittent transfer of ink from an ink fountain roll to an ink distribution system by a ductor roll is widely used in modern printing presses especially offset printing presses because of its high accuracy. As it is known, the ductor roll performs an oscillating movement. It comes in turn in contact with the ink fountain roll and a first ink transfer roll whereby an ink film of a predetermined thickness, width, and length (corresponding to a printing width of the printing press) is transferred along the entire width of the ductor roll. Ink quantity supplied to the ink distribution system in a single stroke of the ductor roll corresponds to the volume of the ink film transferred by the ductor roll.
The rotating ductor roll is subjected alternatively, upon contact with the ink fountain roll and the ink transfer roll, to deceleration and acceleration jolts, respectively. In high-speed printing presses, the number of oscillating strokes in a unit of time is directly proportional to a rotational speed of a printing cylinder and is above the dynamic limit of the inker unit. This results in serious drawbacks. The major drawback consists in that the ink quantity transferred by one oscillating stroke of the ductor roll does not correspond any more to the predetermined ink requirement. Therefore, there is no consistency in ink supply. A further drawback consists in negative influence of the acceleration on the inker- and printing units. An increased oscillation decreases the quality of printing.
As an alternative to intermittently operating inker units, continuously operating film inker units were developed for high-speed rotary printing presses. However, these inker units are extremely sensitive to control, and do not react to ink supply. Drawbacks of these inker units led to development of combined ductor-film inker units, i.e., such as described in German reference No. 3,008,980. However, with these units, it has to be decided how printing work is to be executed, that is whether to use the full press speed and the film inker unit or reduced press speed and a ductor inker unit. The drawback of these combined inker units is increased costs connected with using oscillating mechanisms and adjusting devices. Besides, drawbacks of film inker units still remain.
A film inker unit is disclosed in German publication DE-OS 35 31 433. In this film inker unit, a continuous film transfer band is arranged between the ink fountain roll and the first inker transfer roll. A drawback of this inker unit consists in a relatively high wear of ink rolls and the ink transfer band due to differences in speed between the ink rolls and the ink transfer band. Also, a substantial damaging influence of the heat generated because of continuous frictional contact between the ink transfer band and the ink fountain roll should be taken into account. The abovementioned drawbacks complicate control of film supply in this inker unit.